We plan to continue work on the mechanism of action of B12-coenzymes. We will attempt to establish whether combination of enzyme and apo-enzyme in the absence of substrate results in cleavage of the carbon-cobalt bond. Binding interactions between apo-enzyme and the various intermediates which have been proposed to occur during the catalytic process will be examined. Mechanism of action of plasma amine oxidase. Experiments are now in progress to determine whether a single turnover under anaerobic conditions results in NH ion 4 release. Attempts will be made to identify the structure of the active site through labelling with phenyl cyclopropylamine, a suicide inactivator. The mechanism of action of inactivation of gamma-cystathionase by trifluoroalanine is under investigation. In particular, we are attempting to identify the amino group which is labelled by trifluoroalanine.